Method of developing oil fields



Allg 23, 1932 H. L. DOHERTY 1,872,906

METHOD 0F DEVELOPING OIL FIELDS Filed Aug. 8, 1925 2 Sheets-Sheet 1 H. L. DOHERTY 1,872,906

METHOD OF DEVELOPING OIL FIELDS Aug. 23, 1932.

Filed Aug. 8, 1925 2 sheets-Shet 2 HENRY L. DOHERTY @13 hisv l Patented Aug. 23, 1932 I PATENT oFFIcE `HENRY T.. DOHEETY, 0E NEW Yeux,- N. Y.

METHOD or DEVELOPING oIL rIELDs Application led August 8, 1 925. Serial No. 49,1-28.

This, invention relates to the development of oil elds and more particularly to a method of treating an oil body in the oil sands so that a maximum recovery of oil maybe re'- 5 covered from the sands.

The sand or formation in which the oil is found is seldom of the same de ee of porosity throughout its thickness. ometimes the l upper portions of the sands are more porous lo than the lower portions, or vice versa, or there may be ssures or crevices in the sands which extend in lateral directions. Unless the-oil body occupies the more porous parts of the sand the amount of oil recovered will be but a very small percentage of what might be recovered if the oil saturated sands were those sands of great-.est porosity. Furthermore, if the more porous stratum of the sands are above the general level of the oil saturated 2o sands, the free gas which usually accompanies an oil body will find its way through the upper sands to the wells without carrying or' forcing any oil from the oil body or from the oil saturated sands to the wells. Moreover, even if the oil saturated sands comprise the more porous portions of the sands, the drainage of the oil, which occurs from the top of the sands, will leave an upper stratum of por- 'ou's sands through which the free gas may readily iind its way toward the wells. As a consequence, the gas-oil ratio will gradually increase as the life of the well increases. To

ut the matter in another way, the more oil t at is drained from the top of the oil sands the greater the thickness of the channel or path through which the free gas may flow on its way toward the wells.

It is a well known fact that oil under pressure contains a ver considerablevolume of dissolved gas and at it is theex ansion of the gases in the oil that is primarl y responsible for the movement of the oil through the v sands, the gas expanding and coming out of solution as the pressure decreases. If the free gas which is usually found above the oil body in cavities or domes, is allowed to escape through the sands which have been drained of their oil or through other paths such as channels, crevices or fissures in the sands above ,the oil body, the pressure on the field will fall very rapidly and thus seriously l interfere with the drainage of the oil sands. As the pressure falls the gaswhich is dissolved in the oil will naturally seek the nearest point of low pressure. The upper ortions of the sands from which the oi [has een drained and through which'the free gas is findlng its way toward the wells ywill obviously e the nearestregion of reduced pressurel and consequently the dissolved gas, in 6o expanding, will flow toward this region. Some ofthe oil will be carried up by the expanding gas into this region of reduced pressure and be carried along by the gas which is flowing therethrough toward the wells. However, the top portion of the drained sands will continue to offer a comparatively free path to the iow of gas and consequently the production of oil will gradually decrease while the production of gas will increase.

It is an object of the invention to provide a method of treating the oil bodv which will prevent the free escape of gas through the more porous portions of the sands and thus to increase the amount of oil which may be recovered from the sands.-

Another object is to provide a method of adiusting the position of the oil body within the sands so that the oil may flow through the more porous portions of the sands.

Oil bodies are usually found associated with underlying bodies of water. If the body of water happens to occupy the more porous portions of the sands, the production of oil is very materially retarded or interfered with.

It is therefore a still further object of the invention to provide a method of adjusting the oil body downwardly so as to allow the oil to flow through the more porous stratum therebelow.

The features of the invention will be more fully described in connection with the accompanying drawings in which:-`

Fig. l is a plan view of an oil field in which the oil wells are represented by small circles and the approximate upper and lower bound- .aries of the oil pool underlying the field are respectively the inner and outer dotted contour lines;

Fig. 2 is a vertical sectional view taken on 100 the line 2-2 of Fig. which shows a strata formationfand 011 pool s A ig. a is l view simu to there! ieg-2 showing the.` oil pool after elevation 1n accordance with the process of the mvention;

Fi 4 is a view similar to Fig. 3 showin a m iied strata formation with the oil poo lowld. A c

In practicing the present invention oil wells shown as small circles in Fig. 1 are to be projected into the oil sands accordlng to a more or lessgeometric pattern. While the wells are bein drilled, cores w1ll be taken from the oilsan and a careful study made to ascertain the relative degrees of poroslty -of the sands at different levels. A study of the cores will alsoreveal the relative posimore porous tion of the oil body 12 with res to the arts 14 ofthe san 16. When con 'tions :indicate that .the more porous rtions ofthe sands are above the main yof the oil saturated sands as shown in Fig. 2, the oil body'willbe elevated so as into the sands 16 to bring the level of the oil body-above the upper portion or level of the more porous stratum of sand. vThe elevation of the oil body will be accom lished by pumping water low the oil body; The water will be pumped through water wells located around the edge-water line and also preferably through wells 22 which pro- I V ject through\the oil sands into the' water sands therebelow. It is referred to pumul;

by way of we extending through the oil sands as well as through wells located at 'the edge-water line, so that. the water level 24 ma be raised as rapidly as possible and as uni ormly as possible beneath the entire-oil By raising the level of the oi body in the s manner indicated and until the upper level 26 vthat the volume o of the oil body 'ison a level w1 the more porous stratum 14. (as shownv in Fig. 3), the free gas 28 in the upper portion of the sands will n ot be able t`o escape without doing useful work, namel in forcing or carrying'llie oil'toward the we ls. By elevating the y of oil until theupper part of the porous stratum is completely saturated, it is obvious that the gas pressure on the oil body may be maintained more or less nearly'approximating the original rock .pressure and,

low t e pressure in the region of the wells. As a consequence, the gas, in coming out of solution in the oil, will be .obliged to move laterally toward the wells or in other words, towards the region of reduced pressure. The ratio of as to oil will therefore a proximate more or ess closely gas produced per barrel of oil should not materially exceed the amount of gas which is dissolved in theoil at the pressure existing on the field.

In order to maintain the upper level 26 of shown inFig. 4. If the or above.

lassume that free gas is the ideal rat1o,-which is savanne the oil` bdy substantially sexism., it is contemplated 1n accordance with the invention l that water will be suppliedcontinuousl to' the water sands below the oil body in a ut the same volume that the oil is drained from' Vthe sands. If there is no leakage or migra- `oil recovered from the sands through wells 10 after the oil body has once been raised to the proper level.

If conditions indicate thatthe more porous portions 14 of the sands are .below the oil saturated portions vof the sands, the 'invention contemplates that water shall be pumped from below the oil body through wells 20 suciently .to enable the oil to sink or be forced by the gas pressure thereabove into the more porous stratum 14 therebelow as ressure on the field is comparativel h1 e oil will sink more or less -readi y t roufgxh the water-v wetted sands and gradually onthe field is not very high, the pressure d its `.way to-H I ward the wells 10.- `However, if the pressure.

should be increasedby pumping-gas from an n .extraneous source or by pumping air into the field through wells 30 to assist the oil in penetrating through the water-wetted sands. Once a channel has been established b the oil throu hthe water-wetted sands, the disinae of Yoi will proceed very rapidly and the e ciency .of the oil recovery will be unusually ile it is preferred to obtain cores from the oil sands while the wells are being drilled so that vthe operator may be in a position to adjust the position of the oil both with respect to the more porous stratum or portions of the oil sands, nevertheless the invention may be practiced without this preliminary study ofthe oil sands. The.wells 4may be opened to the iow of oil and gas in the usual manner, the ratio of gas to4 oil being carefully noted. If the wells flow an excessive amount of gas the operator may justifiably through an upperstratum. The operator will then proceed to elevate the oil bo y until the upper level of the `latter'is sufficiently high to prevent the free gas from freely flowm an event, will not be enabled to fall being through such stratum. On the other hand, if the ratio of gas to oil is comparatively lowbut thewells tend to ow a mixture of oil and water, the operator may justiably assume that this stratum of the sands from which the mixture is drawn is o'ccupied at least in part by the body'o'f water and he may therefore roceed to ump out Sullicient Awater toena le the o il gody to sink or penetrate 'into said stratum.

It is preferable that the wells be operated under a back-pressure in order to prevent as far as possible the tendency of the free gas finding lts Y way lio from channeling through the oil body. The maintenance of a back-pressure on the wells is particularly desirable where the'gas pressure on the field is high. Due to the fact that gas will iow through the sands more readily than oil, itv will tend to channel its Way through the` oil sands toward the Wells when the pressure is high.

The invention 1s particularly adapted to the treatment of an oil body orield asawhole'. It also offers a method of recovering oil from oil sands which cannot be satisfactorily drained of their oil by ordinary methods of production. In addition, it offers a method which will enable a more complete extraction of oil from any given oil bearing sands.

What is claimed is 1. The method of developing oil fields which consists in ascertaining the location of the most porous stratum of the sands in which the oil body is found, bringing the oil body into such position with respect to said stratum that the oil will flow through the same toward oil Wells projected into the sands, and maintaining said oil body in line with said porous stratum while removing oil through said wells.

2. The method of developin oil fields which consists in projecting lWe ls into the field in accordance with a given geometric pattern, obtaining cores of the oil sands as the Wells are being drilled, ascertaining from a study of the cores therelative degrees of porosity of the oil sands at different levels and the relative position of the oil body with respect to the more porous strata of the oil sands, changing the relative position of the oil body in the sands to bring the oil body in line with the more porous strata of the sands, and maintaining said oil body in line with said porous strata while recovering oil from said body.

. 3. The method of reducing flow of iuids other than oil along paths in oil sands which are more porous than the main body of the sands which consists in adjusting the position of the oil body into line with the more porous paths in preference to said other liuids and holding the oil body in said new position while flowing oil alon said paths. 4. 4The method of reducing ow of uids other than oil from a regionvof high pressure toward a region of low pressure through paths in oil sands offering relatively low4 resistance to the iow of fluids in the sands which consists in shifting the oil body into a position which will permit the oil to iiow ward a re 'on'of -05 l along the paths of least resistance in preference to the other uids, and holding said oil body in said position while removing oil therefrom. i j

5. The method of preventing gas from owing from a region of high pressure toow pressure along paths in oil san offering lessreslstanoe to the flow of fluids than the main portion of the oil body as a Whole that oil may flow along the most permeable sand stratum toward the sands which consists in elevating the oil body oil Wells in preference to Water and gas, the

position of the oil body being. adjusted by varying the pressure from beneath the same, and lowingoil from said body along said permeable stratum.

7. The method of developing an oil field which consists in projecting Wells into the oil sands, flowing oil and gas from the wells as long as a predetermined ratioof gas to oil is maintained, elevating the oil body in the sands When more gas Hows than should flow according lto said ratio, and maintaining the oil body at that level Whichwill cause the predetermined ratio of gas to oil to be maintained.

8. The method of reducing the water-oil production ratio of an oil Well draining porous sands, which consists in removing the Water from said porous sands and in shifting the underground oil body as a unit downwardly into line with said `porous sands through which the underlying Water tends to flow toward the oil well to thereby cut olf such water flow and substitute a flow of oil therefor.

9. The method of develo ing an oil body contained within sub-sur ace earth strata which consists in shifting the position of the oil body as a unit into line with the most permeable stratum directly communicating with the oil well to thereby increase the flow of oil and proportionately reduce the flow of water and gas.

In testimony whereof lI aix my signature.

- HENRY L. DOHERTY.

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